PK Overdose just does not have that stuff what makes the original Painkiller a superb game in it's class.
Introduction and story: the player is introduced to a new character, that represents a half devil, half angel like creature - Belial. Intro is shown with graphic pictures rather than with a movie-like scene. There is not much to tell - after you are introduced with Belial's story and the basic concept of what you will do - you get started just like in the original game - a wheel of time appears, letting you know how many levels there will be, and then you just start with the first one.
Gameplay: you now have totally new weapons and new levels filled with new monsters, and although the core of gameplay and it's elements remain the same, unfortunately the execution of gameplay is something totally different from the formula of the original game. You move and fight with the same level of furiousness and speed just like in the original game, but now it is both harder and more silly at the same time. Harder it is because the developers made it this way - there feels a total disbalance between your capabilities with the weapons versus what the monsters can do. All the weapons look new, but in fact, act like the original ones just with a "degradation". For example you have a bone made shotgun that fires primary - "bone splinters" and secondary - "fog of slowdown". Basically similar attributes to the original shotgun, but with a worse effect and execution. The same can be said about the new rocket launcher, which fires 3 rockets instead of 1; in fact the new 3 missiles deal the same damage as the original gun and that alone does not really make any sense, and the fact that the chaingun has been replaced by some wana be like "ripple" makes this weapon lame. Original painkiller is replaced with a cube that floats in the air and does the same stuff just with less fashion.. The stakegun is replaced with a pathetic excuse for a weapon - crossbow, that fires 3 arrows, those really have neither power or style. Obviously gone are the grenades and the ability to stake-nade... Electroshaft is replaced with a head that fires lasers from it' eyes and screams damaging voice - all this being said it is clear that the developers not only decreased the quality of the weapons, but also made them look more silly. The new weapons included in the game are not worth mentioning.
The same can be said about the monsters - AI was never a strong part of such games, but this time clearly the developers have made mistakes in the behavior of some of the monsters by making them really either irritating or overpowered. That being said the monsters did not become somehow stronger, but simply their gameplay execution is bad - talk about the likes of plants, fire ghosts or radioactive workers..
Level design: you know that level design in the original Painkiller was exceptional - all levels were made with such a detail, representing real world installations or simply copying them and the architecture was outstanding. In Painkiller Overdose the levels feel more cartoony, certainly have less detail and architecture and more invisible walls as well as buggy places.. However few levels look really nice and have a good gameplay value - particularly Ragnarok and Ghost Valley. Some other levels might look good, but then again, the linearity or the bad gameplay execution in them does not make them good looking overall..
Soundtrack: it is a custom thing really, this time the developers have chosen a more pop-industro like battle music over the more heavy metal riffs of the original game. However the ambient music does not have that amount of greatness and style like the original game had with the exception of the few levels where music is really nice.
Sound: it's ok if we talk about the in-game sounds, but the most irritating thing is obviously Belial's trash talk voice overs. Sam "Serious" Stone at least did not repeat his trash talks every 30 seconds...
Graphics: well what can i say? I mean they look the same as in the Battle Out Of Hell expansion that was released 3 years ago. Certainly this is not good considering that PK Overdose lags alot more than PK Battle Out Of Hell, but at least the graphics are not as bad as in PK Resurrection, where everything is just abysmal...
Competitiveness: the single player offers the same challenges as seen before: the 5 stars challenge, tarot card collection, speedrun, boss time attacks, soul collecting and gold gibing challenges. But it certainly won't feel the same good as in the original.. Speaking of multi player - it is made just for fun. It certainly does not bring the level of skill and competitiveness needed for pro gaming with these new stupid weapons and bad multi player map design.
Customization: it certainly is not a good thing, that game saves as well as cfg files are stored now in hidden Application Data folders instead of game folders. There is also a big problem - in the menu you can not switch the weapons primary/alternative or numerical positions like you want. This is certainly a decrease.
Final words: well, for those like me, who appreciated Painkiller for what it was, this new expansion PK Overdose certainly feels disappointing. It might deliver the same amount of fun just like the original game, but overall PK Overdose became more stupid, less fashionable and appealing, less competitive, more buggy, with a decreased gameplay execution and too late in the gaming market - in the end of 2007.. The best i can say about this game is that it is - still a playable and fun game, certainly not a rip-off and most important - alot better than Painkiller Resurrection..